1. Field of Invention
This invention relates to coating compositions containing colloidal silica and alkoxysilanes, methods of preparation and use, and coated articles.
2. Description of the Prior Art
U.S. Pat. No. 3,976,497 to Clark relates to a paint composition comprising a pigment carried in a vehicle consisting essentially of a dispersion of colloidal silica in a lower aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi(OH).sub.3 in which R is selected from specified groups, at least 70 weight percent of the silanol being CH.sub.3 Si(OH).sub.3. The vehicle contains 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 90 weight percent of the partial condensate. The vehicle further contains sufficient acid to provide a pH in the range of 3.0 to 6.0. While useful for some purposes, these compositions tend to lose adhesion from a steel substrate after curing if applied so as to produce dry film thicknesses greater than about 0.5 mil (1.27.times.10.sup.-5 meters).
U.S. Pat. No. 4,159,206 to Armbruster et al relates to an unpigmented coated composition comprising colloidal silica and a mixture of dialkyldialkoxysilane and alkyltrialkoxysilane such as dimethyldimethoxysilane and methyltrimethoxysilane prepared by adding a mixture of dialkoxysilane and trialkoxysilane, to colloidal silica hydrosols and adjusting the pH with sufficient acid to provide a pH in the range of 3.0 to 6.0.
U.S. Pat. No. 3,986,997 to Clark relates to a pigment-free coating composition comprising essentially the same components as in U.S. Pat. No. 3,976,497 to Clark described above except without pigment.
U.S. Pat. No. 4,197,230 to Baney et al relates to a modification in the pigment-free compositions shown in U.S. Pat. No. 3,986,997 to Clark by incorporation into the Clark composition of at least 1 weight percent of .phi.Si(OH).sub.3 based on the weight of total RSi(OH).sub.3 present in the composition.